Singular spectrum analysis of GRACE...

Singular spectrumanalysis of GRACE

observationsLeonid Zotov1,2 ([email protected]),

C.K. Shum2 ([email protected])

1Sternberg Astronomical Institute, Moscow State University, Russia2School of Earth Sciences, Ohio State University, USA

Gerald North symposiumClimate, Statistics, and Satellites, College Station, June 8-10 2009

We applied the MSSA to monthly GRACE gravity field solutions in both the spatial and spectral domains. The principal components (PC) wereidentified to be related to different physical processes, including seasonal to interannual water mass redistribution, ice/glacial melting, GIA, Sumatra-earthquake. Preliminary results indicate that one could separate noise andsignals using the MSSA approach.

Gravity Recovery and Climate Experiment (GRACE) satellites, launched 17.03.2002, provides an unprecedented set of Earth’s temporal gravity field observations, whose signal manifests as

Earth’s mass redistribution within the Earth system. However, de-stripping/filtering to diminish the correlated high frequency errors is currently required to use the GRACE spherical harmonic data products.

L. Zotov, Climate, Statistics, and Satellites, College Station, June 8-10 2009

MSSA IN APPLICATION TO GRACE MONTHLY DATA

PCAPrincipal

Component Analysis

SSASingular

Spectrum Analysis

MSSAMultichannel

SSA


INITIAL DATA IN SPECTRAL DOMAIN

We used 79 CSR Level-2 RL04 monthly GRACE data since 2002 till 2009 with spherical harmonic coefficients complete to degree 60.

Degree n changes from 2 for the appropriate selection of coordinates.C20 coefficients were excluded in processing. GGM01C model was used as a reference and subtracted. Results are represented in terms of equivalent water height (EWH) levels (mm).

60

2 0)(cos)sin)(cos)((

112

3),,(

n

n

mnmnmnmn

nw

ave PmtsmtcWk

nath

“CATERPILLAR” – SSA METHOD

KXXX ...1Trajectorymatrix

KL

Tddd

TT VUVUUSVX ...111

Singular value decomposition SVD

Principal components grouping

Hankelization


NkKyKN

KkLyL

Lkyk

g

KN

Kkmmkm

L

mmkm

k

mmkm

k

*1

22,

**

12,*

*1

12,

,1

1 ,1

10 ,1

1

*

*

*

11

121

10

21 ],,[

NLL

LN

LN

K

fff

ffffff

xxxX

SIMPLE EXAMPLE OF 1D SSA


0 200 400 600 800 1000

-5

0

5

10

15Initial signallinear trendlow frequency harmonichight frequency harmonic


INITIAL UNFILTERED GRACE DATA (SPATIAL MAP)


Principal Component N1 for MSSA with L=10 in spectral domain


PC 2+3 spectral MSSA, L=10


PC4, spectral MSSA, L=10


Sum of PC 2-10, spectral MSSA L=10


Difference between initial signal and sum of PC 1-10, spectral MSSA L=10

EIGENVALUES

0 20 40 60epoch

1E-019

1E-018

1E-017

1E-016

1E-015

1E-014 Eigenvalues

ω-CORRELATION

Approximation of Stokes coefficient S21 by principal components of MSSA, L=10

0 20 40 60 80

4E-011

8E-011

1.2E-010

1.6E-010

2E-010

2.4E-010

2.8E-010 S21 evolutionS21 approximation by 10 PCPC 1

0 20 40 60 80

-2E-011

-1E-011

0

1E-011

2E-011

3E-011

4E-011 PC 2PC 3PC 4

2002 20092006


PC 2 for MSSA in spatial domain, L=10

Besides MSSA in frequency domain, we applied it in spatial domain to the EWH map (pixel matrix).

Spatial PC 1 is similar to spectral PC 1.

Spatial PC 2 component accumulated the trend.

Spatial PC 3 and 4 correspond to annual oscilletion.


PC 3,4 for spatial MSSA, L=10


Greenland PC 1 spatial MSSA, L=10


Greenland PC 2 spatial MSSA, L=10


Greenland PC 3,4 spatial MSSA, L=10


Greenland PC 2-10 spatial L=10


PC 1 spatial PCA, L=1


PC 2,3 spectral PCA, L=1


INITIAL FILTERED DATA (Gaussian filter R=800km)


PC 1 spatial filtered L=10


Panteleev corrective smoothingIf we have signal u, which passes through the dynamic system (equipment) with transfer function W and gives us observations f together with noise, we can reconstruct u applying inverse operator together with smoothing operator Wsmooth. Smoothing is very important to prevent amplification of noises. If dynamic system is linear, we can write down the corrective smoothing in spectral domain (hat means Fourier transform) as

)(ˆ)()(ˆ)(

)(ˆ fiWf

iWiWu Pantelev

smoothcorrected

Method can be used instead of regularization. We can extract useful information from the signal only if we are able to find basis (functional, vectorial, etc.), where it is separable from the undesirable systematic errors and noise. If we can use SSA basis for denoising and realize Wsmooth in this basis, we would be able to reconstruct the signal usuccessfully. At that, we can apply Wsmooth before or after inversion. if we have been able to decompose Level-2 signal, as it’s shown, we should be able to decompose also the initial unprocessed signal and use this approach for inversion.


1. Rangelova E. et al., Analysis of GRACE time-variable mass redistribution signals over North America by means of principal components analysis, JGR, Vol. 112, 2007;

2. Wouters B., Schrama E., Improved accuracy of GRACE gravity solution through empirical orthogonal function filtering of spherical harmonics. GRL Vol. 34, 2007

3. Golyandina N. et al., Analysis of time series structure: SSA and related techniques, Chapman &Hall, 2001

4. Jollife I.T., Principal Component Analysis, Springer, 2001

5. Panteleev V.L., Algorithms of smoothing of aerogravimetricobservations, correcting dynamic errors of the measurements. Izvestiya RAS, Physics of the solid Earth, N3, 2001 (in Russian)

References


Acknowledgements

To perform this work Ohio Supercomputer Center GLENN cluster wasused. Presentattion at the confernece “Climate, Statistics, andSatellites” was sponsored by NSF. We thank Zhenwei Huang, who helped on initial GRACE dataprocessing. This work is sponsored by RFBR grant 08-02-00256, NASA OSTST, and OSU’s Climate, Water Carbon Program.

Thanks to Jerry North for invitation and hospitality!

Singular spectrum analysis of GRACE...

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